OLED displays require no backlight, and are therefore optimum for thin formation, with no limitation of viewing angle. Thus, OLED displays have become popular substitutes for cathode ray tube (CRT) and liquid crystal display (LCD) devices.
One problem using organic light emitting elements is Mura defect, which is caused mainly by inconsistent luminance of the organic light emitting elements. Luminance of an organic light emitting element is determined in a manufacturing process and degrades with time. The rate of luminance decay of an organic light emitting element depends especially on characteristics of the organic light emitting element, conditions in a manufacturing process, how the organic light emitting element is driven, and other conditions.
Mura defects can be aggravated in full-color OLED display panels that emit red, green, and blue light. The organic light emitting elements of varying colors have different rates of luminance decay. The differences in luminance between the organic light emitting elements of a plurality of colors typically become more apparent with time.
In addition to Mura defects, an OLED display (particularly, the Electro Luminescent (EL) materials) will age and become less efficient at emitting light, reducing the lifetime of the display. The aging of the OLEDs is related to the cumulative current passed through the OLED resulting in reduced performance, also the aging of the OLED material results in an increase in the apparent resistance of the OLED that causes a decrease in the current passing through the OLED at a given voltage. The decrease in current is directly related to the decrease in luminance of the OLED at a given voltage. In addition to the OLED resistance changing with use, the light emitting efficiency of the organic materials is reduced. The different materials may age at different rates, causing “differential color aging” and thus the “shift of white point”. Moreover, each individual pixel may age at different rate than others, resulting in display non-uniformity or so-called “image sticking”.
Conventionally, the Mura defects and the aging of the OLEDs are addressed in separate ways, which make the circuit design complicated and increases the production cost. Therefore, it is desired to have an OLED display and a method for displaying an image in an OLED display, which can compensate the “non-uniformity” resulted from either the Mura defects or the material aging.